Sure, here's an example of a simple game implemented as a single HTML file using JavaScript. The game is a basic emoji merger, where the player combines similar emojis to score points. The game can be played on a smartphone. I'll use pictograms to represent emojis:
In this game, we set up a canvas with a size of 320x480 pixels to display emojis. The emojis are stored in a 2D array and rendered on the canvas. When the player clicks on a group of three horizontally matched emojis, they get cleared from the screen and the score is increased by 10. The score is displayed at the top of the canvas.
Please note that this is a simplified example and you can modify it and add more features to make the game more engaging.